This invention relates to an improved high power short arc gas discharge lamp, and more particularly to such a lamp with improved heat dissipation.
Conventional short arc lamps, using xenon, argon or other gases, produce a broad spectrum light of 200 nm to 1100 nm or more at 1 to 2 Kw using a curved, concave reflector such as a parabolic or elliptical shape surrounding the arc Substantial heat is generated by these devices and can cause rapid electrode erosion and even catastrophic failure. The reflective surface is typically a silvered coating on a ceramic body which electrically insulates the cathode assembly from the anode assembly and the reflective coating from both assemblies. The most intense heat is generated proximate the arc. The heat dissipation problem is exacerbated by the fact that neither the ceramic nor xenon or other gas are very good thermal conductors.
In one approach the heat is removed using a large mass of highly thermally conductive material such as copper or aluminum in the anode assembly. In such devices the mass is somewhat removed from the area of the arc and the heat sink is partly surrounded by Kovar, a material which is approximately only 2% of the thermal conductivity of copper. In another approach the massive copper heat sink in the anode assembly is extended into an internal cavity to contact the wall of the ceramic reflector and conduct heat to the outer wall of the ceramic. This still requires that heat pass twice through the ceramic material before it can be externally dissipated. In addition, the extended portion has a narrow cross-section which acts as a heat choke. In a variation of that approach the second area of ceramic is replaced by a metal heat sink so the heat need travel only once through the ceramic material but the entire heat sink is a part of the anode assembly and is at the same potential which when the trigger pulse is present can be as high as 30 Kv. Here, too, the copper extension is narrow and acts as a thermal choke and the replacement metal heat sink is actually Kovar because of the need to braze it to the ceramic and Kovar has but 2% of the thermal conductivity of copper. See U.S. Pat. Nos. 4,633,128; 5,399,931; 4,599,540; 3,731,133; and 5,721,465.
It is therefore an object of this invention to provide an improved high power short arc gas discharge lamp.
It is a further object of this invention to provide such a high power short arc gas discharge lamp with improved heat dissipation.
It is a further object of this invention to provide such a high power short arc gas discharge lamp which dramatically reduces the possibility of electrode erosion and catastrophic failure.
It is a further object of this invention to provide such a high power short arc gas discharge lamp which locates heat sink material close to the area of the arc.
It is a further object of this invention to provide such a high power short arc gas discharge lamp which reduces the amount of low thermal conductivity material between the area of the arc and heat sink.
It is a further object of this invention to provide such a high power short arc gas discharge lamp which is smaller and more compact.
It is a further object of this invention to provide such a high power short arc gas discharge lamp in which the heat sink is externally mounted yet engages the area closest to the inner reflective surface.
It is a further object of this invention to provide such a high power short arc gas discharge lamp in which the heat sink is electrically isolated from the anode.
The invention results from the realization that a more thermally efficient high power short arc gas discharge lamp can be achieved using an electrical insulating reflector body having a concave internal reflective surface and a conical external surface which reduces the thickness of the body and placing an external, electrically isolated heat sink in conforming engagement with the conical surface proximate the gas discharge gap.
A high power short arc gas discharge lamp includes an electrically insulating reflector body having a concave internal reflector surface with a focal point. There is an anode and a cathode spaced from the anode to create an arc gap between them proximate the focal point. The reflector body has a conical external surface for reducing the thickness of the reflector body between the concave internal surface and the conical external surface. An external electrically isolated heat sink is mounted on the external conical surface proximate the arc gap.
In a preferred embodiment the internal reflector may be a parabolic surface or an elliptical surface. The reflective body thickness may be reduced proximate the arc gap. The heat sink may include a conical mounting surface for conformingly engaging the conical external surface. The heat sink may include a plurality spaced fins and it may be annular.